1. Field of the Invention
The present invention relates to flameless emission spectroscopy and, more particularly, to a sample introduction system for flameless emission spectroscopy which causes complete vaporization and disassociation of a sample.
2. Description of the Prior Art
A variety of methods and systems exist for the quantitative and qualitative detection and analysis of atomic and molecular species in samples, such as body fluids. Two of the more common techniques are emission flame photometry and atomic absorption photometry. In emission flame photometry, the sample is aspirated into a propane flame. The metal ions in the sample absorb heat and are raised to an excited state, the excess energy then being emitted in the form of light as the ions relax to their ground state. The wavelength and intensity of the emitted light are determinative respectively of the identity and concentration of the metallic ions present.
In atomic absorption photometry, a hollow cathode lamp containing the element to be analyzed emits light characteristic of the metallic species. The sample is sprayed into a flame and the light emitted by the hollow cathode lamp is passed through the flame. Neutral metallic species in the flame then absorb the light from the hallow cathode lamp, the amount of light absorbed indicating the concentration of the metallic species being determined. The metallic species currently analyzed by these techniques include sodium, potassium, lithium, calcium, and magnesium.
The principal disadvantage of these and other techniques used for the analysis of the composition of a sample is that the detection apparatus must isolate the light emitted by the sample components against the background of the light emitted by the flame, the latter being substantially greater in intensity. Because of the high intensity of the background light, these techniques have been limited to relatively high concentrations of the sample species.
In order to eliminate this disadvantage, another method has recently been developed for analyzing the elemental or molecular composition of a sample. This technique involves the excitation of the sample atoms through collision with an active metastable PG,3 gaseous species in a Lewis-Rayleigh afterglow, the excited atoms then emitting characteristic wavelengths of light as they relax back to their ground state. Specifically, the sample to be analyzed is introduced into a gas stream containing an excess of an active metastable species of nitrogen or other noble gas whereupon the material, if atomic, is rapidly and repeatedly excited or, if molecular, is decomposed and certain component atoms of the molecule are excited, the excited species emitting characteristic wavelengths of light. The wavelength and intensity of the emitted light are determinative respectively of the identity and concentration of the atoms of the different elements present.
There are at least two advantages to this technique. The first of these is that upon relaxation to the ground state, the atoms may collide again with an active nitrogen molecule, providing that the active nitrogen is present in excess, thereby reexiciting the atom with a subsequent reemission of a characteristic photon. This permits this technique to be used with very low concentrations of atoms. The second advantage is that in contrast to flame photometry or atomic absorption photometry, the background radiation in the Lewis-Rayleigh afterglow region is extremely low in the visible and ultraviolet, permitting the characteristic emission spectra to be observed against a black background. These two advantages combine to make this technique extremely sensitive and capable of extremely good linearity. As a result, a number of systems have been developed utilizing this technique.
When designing a system incorporating this technique, a number of factors must be carefully considered to insure that an accurate result is obtained. Initially, it is necessary to introduce a liquid sample into the discharge chamber in such a way that the sample is completely vaporized and maintained in the gas phase. If a portion of the sample is incompletely vaporized and remains on the sample introduction probe or other means, this portion of the sample may be carried over to a subsequent test and provide an inaccurate result in the subsequent test. In addition, where the introduced sample is molecular, it is necessary to totally disassociate the molecular sample into its atomic components. This is necessary so that the component atoms can be excited into fluorescence. In systems suggested heretofore, one or the other or both of these factors have been inadequately accounted for with the result that the systems have not produced the desired results.